Ironically Miguel entering the coma might be the most vindicating thing about Kreese's way. Remember that if Miguel hadn't shown mercy, maybe Robbie would have gotten a concussion or broken bone and that's it.
Sure, but all that came about because they weren't entirely expecting anyone from Johnny's camp to show leniency, which was around the time Johnny started to see his path may be wrong. In showing leniency, sadly Miguel let his guard down and Robbie's swiftness caught him off-guard and off-balance. And dang man, those floors are some of the hardest floors around. I'm surprised he didn't suffer more damage than he did. That fall was absolutely devastating to watch. So, if anything it only pushed Johnny into realizing what kind of path he was leading his students down into while he was letting them down in the process. Since then, he'd wanted to strive to do better with them. And well, Kreese took over completely and we know how well that went.
I think Daniel perhaps shouldn't have trained Robbie, as it likely only fueled the rivalry leading Johnny to feel bitter about it. Interestingly, I always kind of felt Miguel was more Miyagi-do in terms of philosophy. He didn't strike me as a violent person, but rather someone who'd been let down through a dark path.